Photographic resist and process of photographic etching



Patented Mar. 25, 1930 :UNITED, STATES PATENT OFFICE ALE-x BROOKINGDAVIS, 01? CINCINNATI, OHIO, ASSIGNOR, BY MESNE ASSIGNMENTS,

TO KEYSTONE WATCH CASE CORPORATION, OF

ronarron or rnnnsnvmm no Drawing.

This invention relates to a new resist for photographic purposes and toa novel process of photographic etching.

Of the very considerable number of 5 processes of transferringdecorative designs to metals by means of the usual light sensitiveorgamc resists, a very large proportion have been solutions of organiccompounds in volatile solvents and the deposited organic films haveconsisted of substances which, for the purpose, I may define ashydrophobic colloids. For the purpose of this disclosure that definitionwill be used.

In making a new series of resists it has been found that these newresists may be made and used at a much lower cost than most of the priorresists of the hydro hobic colloid type. These new resists areydrophiles and their solutions are made up in water. In the course ofthe process, however, they become both water and alkali insoluble andmay, therefore, be used for transferring desi s to metals or othersurfaces for decoratlve purposes by etching in 511 lalkaline electrolytein an electroetching It has been known that ordinary shellac is solublein an alkaline etching bath and therefore may not be used as a resisteven :0 though the shellac itself may be somewhat li ht sensitive. It isalso well known that a aline shellac solutions are light sensitive andhave been used for a long period of time in industr where lightsensitivity has been the main actor.

It has been found and proved by experiments that the light sensitivealkaline shellac may be developed by means of tannic acid or tannic-likesubstances to obtain resists 40 Evhilph are insoluble in an alkalineetching In carrying out the process of preparing these new resists andin usin the same for decorative purposes the det-ai ed descriptionthereof is as follows It is preferred to use 5 grams of borax anddissolve it in 100 cc. of water, and to this solution there is added 15grams of powdered bleached wax-free shellac. When the shellac has goneinto solution in the borax, there RIVERSIDE, NEW JERSEY, A COR-rnoroemmc nnsrsr AND :enocnss on rno'roeimrnrc n'rcnine Applicationfiled January 28, 1927. Serial No. 164,380.

is added 5 cc. of 28% ammonia water and then 15 cc. of ammoniumbichromate solution,

made by dissolving 20 grams of crystalline ammonium bichromate in 100cc. of water.

.With the shellac solution made as above described, metal surfaces whichone may desire to decorate, are coated in any desirable manner bypainting on one or more coats, or, for small surfaces, by flowing on thesolution on a spinning table and s inning 01f the excess. The so-coveredsur ace is now exposed toa light image by means of an arc projectionmachine, the light passing through ascreen bearing a design. Thoseportions of the coated surface exposed to the light are renderedinsoluble and the resulting exposed plate is developedbybeingwashed inordinary denatured alcohol, commonly sold as completely denaturedalcohol formula #5, which contains a small quantity of pyridine and woodalcohol in addition to ethyl alcohol. The light exposure time that hasbeen found best is, on an average, one minute, although for small work,good images are obtained in 15 seconds, and the resist is fast for allpractical purposes, therefore.

It has been found to be of advantage to add F to the alcohol used fordeveloping the image a few drops of a dye solution, such for instance asfuchsine dye as the o eration of this dye affords a ready means orjudging the degree of development as it stains the resist.

After development, the plate is dried on a spinning table or by othermeans, and 1s then placed inalcoholic tannic acid made by dissolving 50grams of tannic acid 1n 100 cc. of a solution composed of 50 cc. ofwater and 50 cc. of denatured alcohol. After one to two minutes, thatportion of the resist remaining on the plate has absorbed sufficient ofthe tannic acidto render the shellac insoluble after heating. It is thenremoved and the excess tannic acid washed off in a gentle stream ofwater. Again the work is dried on the spinning table and it is thenbaked on a hot plate until the shellac-tannic acid resist has beenrendered com letely insoluble, and this point may be 1udged by thecolor, which turns to a deep green. Any 100 other parts of the metalwork exposed are now coated with an asphaltum paint and the work maythen be electroetched in a sodium cyanide bath in the known manner.After (etching, the work is completed by removing the resist bydissolving, bulling and polishing.

In the above outlined process, it is to be understood that it is not tobe restricted to the use of pure tannic acid, since tannin-bearing andtannin-like substances may have a similar effect; thus, quebracho andcaoutchouc extracts and other substances capable of combining withalkaline shellac to render it insoluble, have been found suitable. It ispossible to replace the shellac, but with a lesser degree of success inmy hands, with alkaline solutions of kindred natural gums;

' thus, in some degree, an alkaline solution of certain alkali solublecopals, such as Congo, will produce images which can be developed withtannin and tannin-like products.

It is obvious, also, to those skilled in the art, that direct lightthrough a screen superimposed upon the plate bearing the resist, may beused in lace of the arc projection machine, as descri ed above.

The immersion of the developed shellac image in the tannic acid ortannin solution brings about in some measure the insolubility of thecombination and the shellac film definitely absorbs a portion of thetannin, being then in some measure alkali-resistant, but the desireddegree of alkali resistance is usually not reached until the film isheated, whichthereby brings about probably both condensation andpolymerization of the two substances, the resulting polymerized filmbeing practically totally insoluble in all alkaline media gvhiph may beencountered in the etching at x It will be seen from the foregoingdescription that there has been produced a new resist and a new processof photo raphic etching, both of which permit the lesired decorativeeffect on metals by using a much cheaper resist and the process does notrequire the particular care heretofore necessary. It will also be seenthat by the preparation of a resist which is water soluble at thebeginning of the process and which chan es to a water and alkalineinsoluble compoun during the process of manufacturing, a very materialsaving in cost and time are obtained. These advantages are of materialassistance in the practical procedure in decorating metals or otherdesired surfaces, and constitute material improvements over the priorresists and their uses.

It is to be understood that the foregoing description of the improvedresist and the process of use thereof may be varied to some extent, butsuch variations and changes as may be desired are considered as beingwith in the scope of the invention aswould be permitted by the broadinterpretation of the following claims.

What is claimed is 1. As the body of an alkali-insoluble resist forphoto etching, the reaction product of shellac with tannin-bearingsubstances.

2. As a body of an alkali-insoluble resist for photo etching, thereaction product of a light sensitive alkaline shellac withtanninbearing substances.

3. A resist for decorative purposes consisting ofthe reaction product oflight sensitive alkaline shellac and tannic acid.

4:. A resist consisting of a polymer of shellac and tannic acid.

5. As a body of a resist for photo etching, the combination of shellacand tannic acid, the combination being susceptible of subsequentpolymerization to render the same 111- soluble to an alkaline etchingbath.

6. As a body of a resist for photo etching, the reaction product of alight sensitive alkaline shellac and tannin-bearing substance, thecombination being susceptible of subsequent polymerization to render thesame insoluble .to an alkaline etching bath.

7. As a body of a resist for photo etching, the reaction product of alight sensitive alkaline shellac and tannic acid, the combination beingsusceptible of subsequent polymerization to render the same insoluble toan which includes the deposition upon the surface to be decorated of awater-soluble film. which is light sensitive, projecting an imagethereon b means of light, developing the image in enatured alcohol, andsubsequently rendering the image insoluble in alkali by treatment with atannin-containing sub-- stance.

11. The process .of decorating surfaces which includes the depositionupon the surface to be decorated of a water-soluble film which is lightsensitive, projectin an image thereon by means of light, deve oping theimage in denatured alcohol, rendering the image insoluble in alkali bytreatment with a tannin-bearing substance, and subsequently polymerizingthe combination by heat.

12. In the process of decorating metals, the steps of forming an imagein a light sensitive hydrophile which has been placed on the surface tobe decorated, immersing the hydrophile with the image formed therein ina solution of a second hydrophile capable of combining therewith, andrendering the combined film insoluble in alkalis by means of heat.

I 13. In an etching process, the steps of coating a surface to bedecorated with a light sensitive water soluble material, exposing saidmaterial to a projected desi n, developing said material in denatured acohol, rendering said material insoluble to an alkaline so lution,heating said material to condense and polymerize it, and etching.

14. The process of decorating surfaces, the steps of coating a surfacewith a light sensitive alkaline shellac, e osing the same to a lightprojected design, eveloping said coating, subjecting the coating to atannin solution, drying the same, heating the same, and

etching in a solution of sodium cyanide.

15. In the process of decorating metal surfaces, the steps of coatingthe surface with a water soluble solution comprising a light sensitivealkaline shellac, exposing said coating to a design projected by light,adding a small amount of dye material, immersing the coating in tannicacid, removing the same and washing in water, drying the same, bakingthe coating, and etching in a sodium cyanide bath.

This specification signed this 19th day of 30 January, 1927.

ALEX BROOKING DAVIS"

